Stabilized olefin polymer compositions



United States Patent Int. Cl. C08f 45/58 US. Cl. 260-4585 3 ClaimsABSTRACT OF THE DISCLOSURE Organic materials can be stabilized with acompound having the formula:

between 1 and 8; m is a positive integer between 2 and 1 n and m may beequal to each other or not; and D OH, OR, or

where R is an alkyl group having from 1 to 22 carbon atoms.

This application is a division of copending application Ser. No.629,121, filed Apr. 7, 1967, and assigned to the assignee of the presentinvention, now US. Pat. Ser. No. 3,504,012, issued Mar. 31, 1970.

This invention relates to novel compounds and to their use asstabilizers for organic materials. More particularly, this invention isconcerned with the use of these compounds as stabilizers andantioxidants for olefin polymers and to the polymer compositionsstabilized therewith.

A rapidly expanding industry utilizing polyolefin resins has created aneed for stabilizers that will render the finished articles ofmanufacture more useful, more versatile in application, and more nearlypermanent. Polymers of aliphatic olefins have a combination ofproperties, such as high resistance to stress cracking, high tensilestrength, and stability under load, that makes them useful in themanufacture of pipe, film, wire, coatings, or various molded objectssuch as bottles and the like.

These polyolefins, however, are subject to considerable degradation atthe high temperatures that are required in their processing or that maybe encountered by the finished articles. They may also be degraded bychain cleavage resulting from oxidation or attack by acids. Themolecular breakdown which occurs in these polymers during fabrication isusually evidenced by increased brittleness at low temperature andreduced tensile strength and dielectric properties.

It is customary to incorporate small amounts of stabilizers into thepolymer to improve the resistance thereof to thermal and oxidativedegradation, such as various amines, diaryl sulfides, phenoliccompounds, organic phosphites, and the like. Many of the knownstabilizers, however, do not provide the required stabilizing effectwhile others impart undesired color to the stabilized compositions.

In accordance with this invention, it has been found that a variety oforganic materials can be stabilized against thermal and oxidativedegradation by incorporating into 3,538,047 Patented Nov. 3, 1970 rt isa positive integer between 1 and 8; m is a positive integer between 2and 10; n and m may be equal to each other or not; and D=OH, OR, or

O o iR where R is an alkyl radical having from 1 to 22 carbon atomswhich may be straight chain or branched.

The resulting stabilized compositions can be processed under conditionsof elevated temperature and mechanical working without substantialincrease in the melt flow rate and Without important color change.

Specific examples of the stabilizers of this invention include suchcompounds as hydroxyethyl-fi-(3,5-di-t-butyl- 4-hydroxybenzylthio)propionate having the formula IN M T/(CHMhydroxypropyl-B-(3,5-di-t-butyl 4 hydroxybenzylthio) propionate andhydroxybutyl-[3-(3,5-di-t-butyl-4-hydroxybenzylthio) propionate.

Although this invention will be described with regard to the use of thenovel compounds as stabilizers for polyolefins, it is to be understoodthat the compounds are suitable also as stabilizers for other materials,such as elastomers, including both natural and synthetic rubbers;synthetic resins, e.g., vinyl resins, polystyrene, polyamides,polyacetals, and polyesters; fats; gasolines; waxes; soaps; oils;greases; and so forth.

The materials with which this invention will be illustrated are thenormally solid homopolymers and copolymers of aliphatic olefins havingfrom 2 to 8 carbon atoms per molecule, such as ethylene, propylene,l-butene, isobutylene, Z-butene, l-pentene, and l-hexene, and mixturesthereof.

In general, the amount of agent to be added to the polyolefin dependsupon the degree and kind of stabilization desired. The amount ofantioxidant can vary from about 0.001 to about 5.0 percent, based on theweight of the polyolefin, with amounts of approximately 0.05 to 0.5percent being preferred. As a rule, it is preferred to use the minimumamount required to achieve the desired results.

The compounds of this invention can be mixed with the polyolefin in anysuitable manner that will effect thorough distribution and dispersion.This can be accomplished in equipment suitable for mixing solids, as bymilling the polyolefin with the additive on heated rolls such as areused in the compounding of rubber or on other suitable milling or mixingequipment, such as for example a Banbury mixer or conventional rubbermill. Instead of adding the stabilizing agent to the polymer in thesolid or molten state, it can be added to a solution or suspension ofpolymer in an organic solvent or to an aqueous dispersion thereof andthe volatile solvent subsequently removed by vaporization.

The antioxidants of this invention may be supplemented by small amountsof finely dispersed particles of carbon black to shield the polyolefinfrom the deleterious degradative effects of ultraviolet radiation,thereby improving its resistance to light deterioration. Carbon blacksuitable for use herein includes both activated and unactivated types,such as channel carbon black, furnace carbon black, animal or vegetablecarbon black, thermal carbon black, light lamp blacks, acetylene blacks,and the like, and carbon blacks activated in the presence of suchmaterials as oxygen, sulfur, or selenium. The average particle size ofcarbon black used herein should be below about 1000 angstroms andpreferably below about 200 angstroms, so as to ensure a uniformdispersion of the carbon black through the polymer. Amounts of carbonblack within the range of about 0.05 to 5.0 percent by weight of thepolymer, and preferably about 0.1 to 3.0 percent, are satisfactory. Forsome polyethylene applications, carbon black concentrations of up toabout 50 percent by weight can be present, especially where partiallyconductive polyethylene-carbon black compounds are employed.

The preparation of the novel stabilizers and their use of polyethylenein air on a two-roll laboratory mill having a front roll speed of 25r.p.m. and a back roll speed of 35 r.p.m. with the distance between thetwo rolls adjusted to maintain a uniform rolling back in the nip and amill temperature of 320 F. After the polymer started to melt, 300 ppm ofthe antioxidant was added. Samples (75 grams) were taken after 5, 30,60, 90, and 180 minutes, and melt index, weight percent carbonyl, andoxidation induction time were determined. Oxidation induction time wasdetermined by Differential Thermal Analysis (DTA), indicating the degreeof oxidation resistance. The test involves oxidation of the polymer at392 F. and 100 percent oxygen. The analysis measures the length of timebefore oxidation starts. The melt index demonstrates the holdingcharacteristics for the physical properties of the polymer; the carbonylvalues, the holding of the chemical properties.

1 A is polyethylene plus hydroxyethyl-fi-(3,-di-t-butyl-4-hydroxybenzylthio) propionate. 2 B is polyethylene with nostabilizer.

in polyolefin resin compositions are illustrated by the examples whichfollow. It is to be understood, however, that these examples are givensolely for the purpose of illustration and that the invention is not tobe regarded as being limited to any of the specific materials orconditions recited therein except as set forth in the appended claims.

EXAMPLE I 9.2 grams of sodium (0.4 atom) was dissolved in ml. of ethanolin a 500 ml. Erlenmeyer flask equipped with a reflux condenser. When thesolution was complete, the flask was cooled to 10 C. and 60.1 grams ofhydroxyethyl mercaptopropionate (0.4 mole) was quickly added. Thecontents, sodium mercaptide, were placed in a dropping funnel.

Into a 3-necked, 3-liter Morton flask equipped with a stirrer, N inlet,thermometer, reflux condenser and dropping funnel was weighed 101.9grams of the 3,5-di-tbutyl-4-hydroxy benzyl chloride (0.4 mole),prepared by the method disclosed by N. P. Neureiter in J. Org. Chem. 28,3486-90 (1963), dissolved in about 100 ml. of ethanol. The flask washeated to 60 C. and the sodium mercaptide was added dropwise at a fairlyrapid rate. Stirring was continued for about one half hour at 60 C.While still warm, the solution was filtered to remove the NaCl which wasrecovered in stoichiometric amounts (0.4 mole). The filtrate wasdistilled under Water pump vacuum to remove the alcohol.

The product was identified as hydroxyethyl-5-(3,5-di-tbutyl-4-hydroxybenzylthio) propionate.

Analysis.-Calcd. (percent): C, 65.18; H, 8.75; S, 8.70. Found (percent):C, 65.35; H, 8.91; S, 8.50.

A satisfactory antioxidant should hold the chemical and physicalproperties of the original organic material during an acceleratedoxidation testing procedure, generally up to three hours duration. Forthe following examples, the test procedure consisted of milling onepound As can be seen from these data, polyethylene with no stabilizer(Sample B) shows poor mill stability and high carbonyl formation at afast rate. Sample A containing the same polyethylene as Sample B plus astabilizing compound of this invention is seen to have retained itschemical and physical properties as judged by the data for melt index,weight per cent of C=O, and oxidation induction time (DTA), thusdemonstrating the effectiveness of this compound as a stabilizer.

What is claimed is:

1. A stable composition comprising a polymer of an aliphatic olefinhaving from 2 to 8 carbon atoms per molecule and from about 0.001 toabout 5.0 percent by weight, based on the polymer, of a compound havingthe formula:

wherein m is a positive integer between 2 and 10.

2. The composition of claim 1 wherein the compound is hydroxyethyl,8-(3,5-di-t-butyl-4-hydroxybenzylthio) propionate.

3. The composition of claim 1 wherein the olefin is ethylene.

References Cited UNITED STATES PATENTS 3,242,135 3/1966 Bbwn 26045.85

HOSEA E. TAYLOR, Primary Examiner V. P. HOKE, Assistant Examiner U.S.Cl. X.R.

